[Raellus]

"Surplus armor" owned by civilian citizens would probably be overlooked by the military until things started to get really bad (post-TDM). At that point, private collections near military installations would probably be commandeered, restored, and used in some capacity. Collections in out-of-the-way places might be commandeered by civilian defense forces or aspiring warlords. Whether such groups could actually operate said vehicles is an open question.

As several folks have already pointed out, keeping such vehicles up and running is going to be rather difficult and it's likely that many of them are going to end up as static pillboxes or showpieces sooner or later.

I figure most such private collections are very small (one or two vehicles at most) but there are a couple of very large collections here in the U.S. There's at least one such mega-collection in Nevada, I believe. There was an AFV restoration show on Military Channel or Discovery a couple of years back that featured several vehicles acquired and restored by a wealthy patron's hand-picked crew. They had all kinds of WWII and Cold-War era AFVs- everything from a Hellcat TD to a fomer target-range Sherman to a Centurion MBT to a German Panther recovered from a Polish river. All were restored to operational condition.